1. Technical Field
The present invention relates to a method of producing trioxane.
2. Description of the Related Art
Polyoxymethylene, which is an engineering plastic, is prepared from trioxane. A variety of trioxane synthesis methods have been known to date. In particular, synthesis of trioxane by heating formaldehyde in the presence of an acid catalyst is mainly utilized.
Without regard to the synthesis methods, trioxane is obtained in the form of, not a pure material, a mixture comprising formaldehyde, small amounts of other components (e.g. methanol, methyl formate, methyl aldehyde and formic acid), and a large amount of water. Pure trioxane is required to prepare polyoxymethylene. To this end, diverse processes such as distillation, extraction, distillative extraction, and pressure swing distillation are disclosed.
As for production of trioxane using distillation evaporation, a large amount of water is inevitably contained due to vapor-liquid equilibrium of trioxane-formaldehyde-water. Since evaporation of water is accompanied by a loss of a very large amount of evaporation heat, the energy necessary for production of trioxane is increased.
To reuse some of the energy consumed as the evaporation heat, Korean Patent Application No. 2010-0107119 and Japanese Patent Application No. 1981-084832 disclose a method of extracting trioxane with an organic solvent from a gaseous distillate via distillative extraction. However, these patents are problematic because the mixture comprising trioxane, formaldehyde, and water, with latent heat, is fed in a gas phase into an extraction column, making it impossible to utilize latent heat as energy.
Separation of trioxane from the gas mixture comprising trioxane, formaldehyde, and water needs a large amount of energy to undergo a phase change. Hence, Japanese Patent Application No. 1992-208265 discloses a method of extracting trioxane synthesized in the presence of a solid catalyst, using a solvent having a boiling point higher than that of trioxane, without the use of a distillation column, namely, without phase change. However, trioxane, which has high solubility in water, may remain, to a large degree, in an aqueous phase. To reduce the amount of trioxane in an aqueous phase, Japanese Patent Application No. 1992-208265 discloses the use of at least 2800 ml of a solvent to extract 1 g of trioxane. When a large amount of solvent is employed in this way, a large-sized distillation column is required for the subsequent process for separating trioxane and the solvent, and a great amount of energy is also consumed.
For conventional separation of the mixture comprising formaldehyde, water, and trioxane, phase change into a gas phase and then distillation are performed. As such, a large amount of energy is undesirably consumed during phase change. Furthermore, the case where liquid/liquid extraction is carried out without phase change is problematic because a large amount of trioxane is transferred to an aqueous phase, undesirably deteriorating processing efficiency.